As a load device, there can be mentioned a constant current load device such as a resistor, which consumes a constant current, and a PWM load device such as an TED light, in which a drive voltage or a drive current is controlled in a PWM mode. Here, the PWM mode is a mode, in which an output of an electrical signal, such as a voltage and a current, is turned ON and OFF, to thereby generate a rectangular wave pulse signal, and then the load device is controlled by the pulse signal concerned.
In the case of attempting to detect a fault of the constant current load device, such as an overload state, a short circuit of the load and an unconnected state, investigation as to whether or not there is a current to be consumed in the load is performed at arbitrary timing. Meanwhile, in Patent Document 1, it is disclosed that, in the case of attempting to detect a fault of the PWM load device, a consumption current thereof is periodically sampled a plurality of times, a predetermined arithmetic operation is performed by using all results of the sampling, and a result of the arithmetic operation is used appropriately.
Note that, in general, two types can be mentioned as a driving method of the PWM load device. One is a driving method, in which the drive voltage is controlled in the PWM mode, and is supplied to the load device. In this case, in response to the supplied voltage, the load device consumes the current (that is, flows the drive current) in a period when the voltage is ON. Other is a driving method, in which, though a constant voltage is supplied, the drive current is controlled in the PWM mode and is supplied to the load device. In either case of the driving methods, a consumption current subjected to the pulse width modulation, which corresponds to a PWM drive, flows through the load device.